Today, secondary batteries have been widely used from large devices such as a vehicle and a power storage system to small devices such as a mobile phone, a camcorder, and a laptop.
As the application field of the secondary batteries becomes wider, the demand for improved safety and high performance of the battery has been increased.
A lithium secondary battery which is one of the secondary batteries has an advantage that energy density is higher and a capacity per unit area is larger than a nickel-manganese battery or a nickel-cadmium battery.
However, most of the electrolytes used in the lithium secondary batteries in the related art are liquid electrolytes such as organic solvents. Accordingly, safety problems such as leakage of electrolytes and the risk of fire resulting therefrom have been constantly raised.
As a result, recently, to increase safety, an interest in all-solid-state batteries using solid electrolytes rather than liquid electrolytes as the electrolytes has been increased.
The solid electrolyte has higher safety than the liquid electrolyte due to a non-combustible or flame-retardant property.
The solid electrolytes are divided into an oxide-based electrolyte and a sulfide-based electrolyte. The sulfide-based solid electrolyte has high lithium-ionic conductivity compared to the oxide-based solid electrolyte and is stable in a wide voltage range and thus the sulfide-based solid electrolyte is frequently used.
In Korean Patent Application Publication No. 10-2008-0069236, there is disclosed a manufacturing method of a sulfide-based solid electrolyte in which lithium sulfide and diphosphorus pentasulfide are milled for a predetermined time by a mechanical milling method to obtain sulfide glass and then the sulfide glass is heat-treated. In the manufacturing of a sulfide-based solid electrolyte through a dry process, there are problems below.
The mechanical milling in the dry state is performed for hours while materials sensitive to oxygen and moisture such as lithium sulfide and diphosphorus pentasulfide are exposed outside for a long time, and thus a physical property of the sulfide-based solid electrolyte as the final material deteriorates.
Since the materials are easily cohered on the wall surface of the container used in the mechanical milling, physical energy is not evenly applied to the materials and thus a difference in amorphization between sulfide-based solid electrolyte particles (powder) is caused, and further, the physical properties of the sulfide-based solid electrolyte become nonuniform during crystallization through heat-treatment.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.